Tire mold



Oct. 4, 1932.

A. R, FURNAS Filed Feb. 14, 1931 2 Sheets-Sheet l Oct. 4, 1932. A. R.FURNAS 1,880,430

TTTT MOLD Filed Feb. 14, 1931 2 Sheets-Sheet 2 INVENTOR A 4? f. fie/v19:

ATTORNEYS Patented Oct. 4, 1932 AUBREY R. FURNAS, F UNIONTOWN, OHIO,

ASSIGNOR TO THE FIRESTOINE TIRE &

RUBBER COMPANY, OF AKRON, OHIO, A CORPORATION OF OHIO TIRE MornApplication filed February 14, 1931. Serial No. 515,780.

This invention relates to tire molds and methods of making tires andmore especially it relates to apparatus and procedure for makingpneumatic tire casings.

Tires of the character mentioned usually are formed with distinctive andcharacteristic tread configurations which serve to identify the tire,and to prevent skidding "on slippery pavements. The tread design usuallycomprises suitably shaped lugs or ribs separated by grooves, and in somedesigns the lugs are isolated, that is, completely separated fromadjacent lugs. In such cases it is customary to interconnect thelug-forming recesses in the cavity of the tire mold by means of narrowkerfs or slots to permit air, entrapped in said recesses during themolding of a tire, to flow to the margin of the mold cavity and toescape from the mold at the meeting plane between the upper and lowersections thereof.

Tires vulcanized in molds of this kind have narrow webs of rubberconnecting the respective lugs of their tread structure, which Webs areformed bygthe venting kerfs. Because of the narrow width of the kerfs,there is consiclerable. frictional resistance to the flow of the rubberthereinto; with the result that frequently the kerfs are not completelyfilled with rubber and the resulting lug-connecting webs of the tire areincomplete,'usually being notched in their outer, unattached margins. Inuse, the flexing of the tire splits the webs,-

the splits starting at the apex of the notches in the webs and extendingto the bottom of the webs and into the body structure of the tire tread,resulting in premature failure of the tire. r I V V V The chief objectsof this invention are to prevent premature failure of pneumatic tiresfrom tread cracking; to produce pneumatic tire casings having treaddesigns comprising isolated characters or lugs without websinterconnecting said lugs; to provide a suitable mold for use inproducing tires of such construction; and to provide a novel,economical,

and elficient method of making such tires.

Of the accompanying drawings: Figure 1 is a fragmentary elevation oftheouter periphery of a molding cavity in a tire mold embodying and adaptedto carry out the invention in its preferred form;

' Figure 2 is a section on a smaller scale on line.22 of Figure 1; sFigure 3 is a fragmentary transverse section ofa finished tire madeaccording to the improved method 1 s Figure 4: is a view similar toFigure 1 of a modified form of the improved mold;

Figure 5 is a section, on a smaller scale, on the line 5-5 of Figure1;and j Figure 6 is a fragmentary transverse section of a tire made inthe modified mold.

Referring to Figures 1 and 2 of the draw- 7 ings, the improved tire moldconsists of a pair of annular mating mold sections 10, 11 which areinteriorly formed with a molding cavity 12 for a pneumatic tire casing,and in the embodiment shown the mold sections meet at a plane 13 whichis disposed at one side of the medial plane of the molding cavity 12.The outer peripheral wall of the cavity 12 is formed with isolatedrecesses 14,

14 which are defined by intervening ribs 15,

15, said recesses being adapted to form the lugs or characters of thetread portion of a tire, the ribs 15 forming the grooves thereb'etween.Such a tire is shown in'Figure 3 wherein 16 is a tire carcass, 17 thetread portion thereof, 18, 18 the grooves formed in said tread, and 19,19 the lugs defined by said grooves. 7

Formed in each mold section, at suitable intervals circumferentially ofthe cavity 12 therein, are kerfs or slots 20, 20 which preferably are'concentric with the transverse radius of the cavity at the outerperiphery thereof, said kerfs extending from the respective shoulders21, 21 of thetread-forming portion of the cavity to the parting plane 13of the mold. The kerfs 20 cut through the intervening ribs 15 and areof'greater depth than the recesses l4c'so as to penetrate the moldstructure below the bottom ofthe recesses, as is clearly shown in Figure2.

In the slots formed by the kerfs 20 in the ribs. 15 are mounted fillers22, 22 which consist of metal plates of the same general contour as theribs. That margin of each filler 22 thate'xtends below the bottom of there cesses 14 is tapered or oppositely inclined from its middle, as isshown in Figure 2, the apex of the taper being slightly spaced (aboutinch) away from the bottom of the kerf. The arrangement is such that airentrapped in the recesses 14% of the molding cavity during themountingof a tire therein can escape from the recesses by means of the kerfs 20in the usual manner since the continuity of the kerfs is not entirelyobstructed by the fillers 22. o o v 7 Tires are vulcanized in theimproved molds in the usual manner, and during the vulcanizing of thetires the tread-rubber thereof flows into the kerfs 20 and around thetapered ends of the fillers 22, forming low transverse ribs 23011 thetread of the tire as indicated in broken lines in Figure 3. In removingthe tires from the molds, the thin portions of the ,ribs 23' which:overlie the tapered edges of the fillers 22 are readily broken so thatno difliculty is encountered in r m ing the tire. l V a The ribs 23subsequently are removed from the tire by bn'tfing- [In the finishedtire th e are no webs spanning the grooves 18 therein, and the bottomsof the latter are rounded as shown so that th re is no tendency fortread-cracks to start in the grooves. I In the modification shown inFigures 4, 5 and 6 mold sections 25,2Ga1e formed interiorly with a tiremolding cavity 27, the medial plane of thecavitybeing coincident withthepar ing la 28-of thein d e tions. The head orming regionof the-cavity27 is formed with visolated recesses 29,

.29 h h are defined by inte veni g rib 30, 30 similar to recessesandribs of the preferred structure. l r 1 The recesses 29 remote from thepart ng plane'28 are connected to the recesses con iguous, there ith byker s 31,- 31 which transect the ribs 30, the bOttQmS-ofthe kerfsbeingflush with the bottoms of the recesses. M nted in the kerfs 31amfillers 32, 32 which conform generally to the contour of the ribs 30.The fillers extend almost tothe o oms of the kerfs, and have t eir bot-trgins ap ed 1? opp sitely inclined from the middle; he pex o t e pebeingsl ght.- ly spaced from the mold wall,as is clearly shown in Figure5 o provide aperture through theribs 3O fronionerecess 29 to anothe Thearrang me t effects the: venting of ent apped air fr m the moldingcavity 27 during the mOlding of a tire. Y

tire vul a ized in thelmodified-m l structure is'shown at 35, Figure 6,thetread portion of the tire comprising lugs '36,- 36

defined by intervening grooves 37, 37. 1

Spanning the grooves 37 are small strands or ribs of rubber 38 which areintegral with the lugs 36, said strands being formed by the flow ofrubber into the vent apertures beneath the fillers 32, the strands beingcen-- 8. A tire mold as defined in trally ruptured as shown during theremoval of the tire from the mold. The strands 38 serve no function andhave no eifecton the vening ribs at the tread-molding region thereof,said recesses being interconnected for ventlng purposes by kerfs 1nthebottoms of the recesses, which kerfs extend beneath the said ribs. II

3. A tire. mold as defined-in claim 2 in which the kerfs are ofrestricted area beneath the ribs. x V v 4:. A tire mold comprisingmating mold sections formed interiorly with a molding cavity includingrecesses defined by intervening ribs at the tread-molding regionthereof, said recesses being interconnected for venting purposes bykerfs which transect said ribs, and fillers in the kerfs in said ribs,said fillersbeing so constructed and ar rangedas to define aperturesthrough the ribs at the base thereoff v l 5. A tire mold as definediinclaim 4: in which the fillers are so shaped that the ventconstricted. VI

Zing apertures defined thereby are locally ,6. A tiremold as defined inclaim l in whichthe bottom margins of the kerfs are herfs are centrallyconstricted.

7 A tire mold comprising mating mold sections formed interiorlyc withamolding thereof, sald recesses being interconnected for vent ngpurpose's'by kerfs which transect said ribs and extend below the bottomsof the recesses, and fillers mounted in the kerfs in said ribsdefining'through passagc'sbelow the bottoms of the ribs. 7

claim 7 in which each filler has a projecting portion ext'ending intothe passage below the rib and locally constricting said passage.

which each filler has a margin that is tapered to a point, said taperedvportion extending into the'passage below the rib and locallyconstricting the same.

AUBREY R. FURNAS.

9. A tire mold as defined in claim 7'in tapered so that the aperturesdefined by the

